Electronic products have revolutionized the world over the past few decades with personal computers, laptop computers, palm top computers, personal digital assistants, wireless phones, pagers, modems, cellular phones, digital cameras, cellular phones with internet access, cellular phones with digital cameras to name just a few electronic products developed in recent years. These products are continually becoming more and more compact, while providing more enhanced features and functions than ever before. The integrated circuit (IC) chip and the more efficient packaging of the IC chip have played pivotal roles in the enhanced functions and miniaturization of these products.
The IC chip must be able to communicate with other chips and circuits on a printed circuit board through an Input/Output (I/O) system with interconnections. Moreover, the IC chip and its embedded circuitry are delicate and must be protected. A package functions to protect an IC chip from environmental elements, to provide a path for the electrical current that powers the circuitry on the chip, to distribute the signals on to and off of the chip, and to remove heat generated by the circuitry on the chip.
As IC chips become more and more complex and printed circuit boards become more and more crowded, IC packages continually need more leads or pins to support the I/O and power requirements of the complex IC chips. At the same time, IC packages are becoming smaller and smaller. The industry's answer to this has been the ball grid array (BGA) package.
A typical BGA package includes an IC affixed to an interposer. A thin conductor or wire bond connects a pad on the IC to a conductive trace on the interposer. The conductive trace is routed to a solder ball. The solder ball is one of an array of solder balls mounted to the opposite side of the interposer and protruding from the bottom of the BGA package. These solder balls interconnect with an array of pads located on a substrate, such as a printed circuit board. Accordingly, the typical BGA package electrically connects each pad on an IC to a pad on a printed circuit board.
One problem with integrated circuits, including BGA packaged ICs, is that they require precise temperature control for efficient operation and reliability. Thus, if a package runs too hot, the heat can affect the performance and timing or the device, and reduce the lifetime of the IC. Accordingly, there is a need for an effective way to maintain control over the temperature of a device and keep it cool.
In high speed applications, electrical interconnections associated with the IC chip, the interposer, and the board interconnections of a BGA can result in degradation of signal quality, which generally increase as signal frequencies increase or as interconnections become longer or closer together. In the past, discrete resistors and capacitors have been placed outside of the package in the signal path to reduce or eliminate unwanted resonances and signal reflections. However, placing these components outside of the package limits their electrical performance, and additional cost, weight, assembly complexity, and reduced circuit density are incurred with the use of discrete resistors and capacitors.
Also, there is a need for a cost effective improved wire bonding electrical performance, thermal performance, transmission line impedance, low package thickness, integrated passive components, surface mounted components and the ability to mount multiple ICs or discrete components within a single BGA package.